Rheostat



Oct. 5, 1954 D. J. HOLLERAN RHEOSTAT 4 Sheets-Sheet l Filed Feb. 24, 1951 Oct. 5, 1954 D. J. HoLLERAN 2,691,087

RHEOSTAT Filed Feb. 24, 1951 4 'sheets-sheet 2 Oct. 5, 1954 D. J. HOLLERAN RHEOSTAT 4 Sheets-Sheetl 3 Filed Feb. 24, 1951 Oct. 5, 1954 D. J. HOLLERAN 2,691,087

RHEOSTAT Filed Feb. 24, 1951 4 sheets-sheet 4 Patented Oct. 5, 1954 UNITED STATES .412., OFFICE RHEOSTAT Application February 2li, 1951, Serial No. 212,553

(Cl. 20L-48) Claims.

This invention relates to rheostats oi the type including a dielectric base and a resistance winding mounted on a dielectric core which is xedly secured on said base, and more particularly the invention contemplates such rheostats having` ceramic bases and ceramic split ring cores.

One object of the invention is to provide a rheostat wherein the resistance element comprising the core and the winding thereon shall be secured to the base in a novel and improved manner, whereby said base and core can be rapidly, simply and neatly assembled and a bond oi great mechanical strength between the parts shall be possible.

Another object is to provide such a rheostat wherein the base shall have an integral upstanding post to which the ring core is bonded as by vitreous enamel, in encircling relation thereto, so that said post and said core are in effect integrally associated and rapid conduction or dissipation of heat from the resistance winding is ensured to keep the rheostat cool.

It is known that the wattage rating of rheostats of this type must be such that the core and base will not become excessively heated or heated to such degree as to become fire hazards, and consequently it has been the practice to make the rheostats of certain sizes as to ensure safety at given wattages, a relatively small wattage requiring a larger rheostat than is desirable. It is preferred that the rheostats be compact and small, and therefore a further object of the invention is to provide a rheostat which shall em- 'body novel and improved features of construction for Ventilating or quickly dissipating heat from the base and core, whereby a rheostat of a given size shall have a higher wattage rating than known rheostats of the same size.

In rheostats of the aforesaid type, a contact arm swings or rotates coaxially with said core to move two brushes over said resistance winding and along a concentric annular contact member respectively, and further objects of the invention are to provide a novel and improved stop on the base at the ends of -said split ring core to be abutted by said contact arm for limiting the rotation thereof in both directions; and to provide means which shall serve'both as said stop and to clamp said annular contact member on said base and which can be accurately positioned and easil3T assembled with the base and the contact member.

Other objects, advantages and results of the invention will be brought out by the following description in conjunction with the accompanying drawings in which Figure 1 is a plan view of one end of a rheostat embodying the invention with the operating knob removed;

Figure 2 is a similar View of the other end of the rheostat with portions broken away approximately on the plane oi line 2-2 of Figure 4;

Figure 3 is a vertical sectional View approximately on the plane of the line 3-3 of Figure 2;

Figure 4 is a similar view taken on a plane approximately perpendicular to the plane of the line 4 4 of Figure 3;

Figure 5 is a fragmentary side elevational View of the rheostat approximately on the plane oi the line 5-5 of Figure 1;

Figure 6 is a plan view of the base of the rheostat with the stop lug for the contact arm removed; f

Figure 7 is a bottom plan View of the stop member for the contact arm;

Figure 8 is a fragmentary plan view similar to Figure 6, showing a modified form of the base;

Figures 9, 10 and 11 are similar views showing additional modifications of the base;

Figure 12 is a View similar to Figure 6 showing another form of the base;

Figure 13 is a plan View of one form of the split ring core for the resistance winding with portions broken away and shown in section;

Figure 14 is a vertical sectional view approximately cn the plane of the line iii- Ml of Figure 13;

Figure l5 is a view similar to Figure 13 showing another modification of the core;

Figure 16 is a sectional view on the plane of the line iii-H5 of Figure 15;

Figure 1'7 is a View similar to Figure 13 showing another modication of the core;

Figure 18 is a vertical sectional view approximately on the plane of the line lf3-i8 of Figure 17;

Figure 19 is a View similar to Figure 17 showing another modification of the core;

Figure 20 is a transverse sectional view on the plane of the line 2li-2li of Figure 19;

Figure 21 is a view like Figure 17 showing another form of the core;

Figure 22 is a transverse view on the plane of the line Z-E' of Figure 21;

Figure 23 is a plan View of still another form or" the core;

Figure 24 is a sectional view on the plane of the line 2li- 2li of Figure 23;

Figure 25 is a view like Figure 23 showing a further modification of the core;

Figure 26 is a sectional View on the plane of the line 26--26 of Figure 25;

Figure 27 is a plan view of another form of the core;

Figure 28 is a sectional view on the plane of the line 28--28 of Figure 27;

Figure 29 is a fragmentary perspective view of one end of the split ring core and one of the terminal clips;

Figure 30 is a fragmentary vertical sectional View similar to Figure 3 showing another form of stop for the contact arm; and

Figure 31 is a horizontal sectional view approximately on the plane of the line 3|-3I of Figure 30.

Specifically describing the lembodiment of the invention illustrated in Figures 1 to 6 inclusive, the reference character A designates the -base of the rheostat which has a flange I at one end thereof and a central post 2 from which a sector shaped projection 3 extends outwardly to the periphery ofthe flange I, the base being formed ofsuitable dielectric high heat-resisting, preferably ceramic, material. The post 2 may be substantially cylindrical, except for the sector shaped projection 3, vbut preferably is slightly smaller in diameter Aat its outer end than at its juncture with the flange I.

A split ring core VB of the same material as the base A, is provided for theresistance winding 4 of suitable material which is connected at its ends and at the ends of the split ring .core to terminal clips 5 which are secured to the core by rivets or other suitable fasteners 5a. The core is secured to the base A in closely spaced encircling relation to the post 2, abutting the vflange I and with its end disposed at opposite sides of the projection 3 of the base.

In accordance with the invention, the core is bonded or secured on the base by a layer E of suitable fusible ceramic material such as vitreous enamel between the post and the inner surface of the core throughout the major portion of the height of the core. Preferably the peripheral surfaces of the winding 4 are valso coated with vitreous enamel 4b, but the end of the core and the winding thereon abutting the flange I is uncoated as is also the opposite end of 'the core and the winding which provides a track or contact surface 4a for a brush I which is carried by one end of a contact arm C the other end of which has a brush 8 frictionally slidable along an annular contact member 9 seated on the free end of the post 2.

The lcontact arm may be of any .suitable construction but is shown as comprising a metal plate I formed with two holes Illa each to receive one arm II projecting from one side of a disc I2 which is secured by rivets I3 to a cylindrical ceramic block I4 which is in turn fast connected to an operating shaft I by a disc I6 which is secured to the cylindrical block by rivets I'I. The contact arm vplate II) is normally held in engagement with the arms II of the disc l2 by a pin I8 having a head I9 at one end thereof normally seated at one end of a slot 2u in the plate Il] and having a head 2I at its other end between which and the disc I2 is interposed a spring 22 which normally pulls the plate I0 toward the disc I2 and presses the brushes 8 and 'I into frictional contact with the annular contact member 9 and with the track surface on the resistance winding, respectively.

The brushes may be of any suitable material, for example a combination of graphite and a finely divided metal such as copper.

The operating shaft lI5 is shown as journaled in a bearing sleeve 23 that has a polygonal head at one end seated in a correspondingly shaped socket 24 in the bottom wall of a recess 25 in which the cylindrical block I4 is located; and the sleeve is exteriorly threaded and has a nut 2S thereon for securing the sleeve in position on 'the base. At its outer end, the operating shaft I5 has a split spring stop ring 2'! to abut the end of the sleeve 23, and a concave-convex spring 28 is interposed between the bottom of the recess 25 and the disc Iii to hold the stop 21 in snug contact with the sleeve and thus take up all looseness between the parts. A knob 2S is attached to the outer extremity of the shaft for rotating the latter.

In accordance with another feature of the invention, the top of the projection 4 terminates below the plane of the outer end of the core B and has a groove 33 in which lies the terminal arm 3i of the 'annular contact member 3. This arm is xedly clamped in position by a combined clamping and stop block 32 which has a rib 33 on vits underside to t into the groove 3D and abut the farm 3| as shown in Figure 4, the block being of a height .to project above the brush track surface of the core so as to be in the path of movement of the contact arm plate I0 and thereby serve asa stop to limit rotation of the contact-arm in both directions. The block 32 may be fastened to the base in any suitable manner, as by a bolt 34.

In order to provide a more secure bond between the core 4 and the post 2, the side surfaces of the post may be roughened or formed with projections or grooves, for 'example as shown in Figures 8 and 9 where V-shaped and undercut grooves 2a and 2b are shown respectively. In Figure 11 another form of grooves 2c is shown while Figure l0 illustrates a plurality of circumferentially spaced fins or projections 2d.

Another feature of the invention is the provision of means for Ventilating or ensuring rapid cooling of the rheostat, particularly the core 4. As shown in Figures 1 to 7, inclusive, the core 4 is provided with a plurality of longitudinal holes 35 that open through both ends of the core and register with corresponding holes 36 that extend transversely through the flange I of the base. With this construction, air may freely circulate through the holes 35 and-35 and thereby effectively vmaintain the rheostat in cool condition. In order to compensate for any chance misalignment of the holes 35 and 36, an arcuate groove 3'I may be formed in the ange I at the inner ends of the holes 36 so as to provide a continuous annular channel for the circulation of air from the holes 36 to the holes 35.

In addition to cooling the rheostat, it will be observed that the holes 35 will allow refuse or particles from the brush I to slip between the convolutions of the winding, especially when the rheostat is disposed with the brush at the upper end thereof, and the portions of the wire convolutions that traverse the holes 35 are also cooled. Furthermore, the portions of the wire that cross the grooves have a "give or resiliency under the pressure exerted thereon by the brush I so as to provide an easy running contact of the brush with the Winding 'and minimize the need for a lubricant on the track surface 4a.

The formation and location of the Ventilating passages or channels in lthe base and core may be Widely .modied For example as shown in Figure 13 an arcuate groove or channel 38 -is formed in the core D insteadcf the holes 435, said channel opening through the bottom surface of the core or the surface thereof that abuts the base iiange l, and also opening through the ends of the core. With this form of the invention, the air will be supplied through the openings in the base into and through the channel.

Figure shows the core E as formed with a plurality of circumferentially shaped slots 3s instead of the cylindrical holes Figure 12 shows a modification of the base wherein the flange is provided with circumferentially spaced slots Il@ corresponding to the slots 38 of the core E. In Figure 17 is shown a form of core F similar to that shown in Figure 13 eX- cept that the annular groove d! terminates short of the ends of the core.

Figures 19 and 2.0 show an annular groove 42 opening through the end of the core G' at which the brush track surface is formed instead of through the end of the core that abuts the base ange l as shown in Figures 17 and 18.

Figures 21 and 22 show the core I-I as provided with a plurality of cylindrical holes t3 extending from the end of the core that abuts the base flange inwardly only a portion of the thickness of the core and communicating with a plurality of cylindrical holes fill that extend inwardly from the opposite end of the core.

In Figures 23 and 2li a similar core I is shown with the exception that the openings i8 correspending to the openings til are disposed at the end of the core that abuts the base flange l while the arcuate groove i9 is disposed at the brush track surface end of the core.

Figures 25 and 26 illustrate a core K in general similar to that shown in Figures 23 and 24 with the exception that a plurality of circumferentially spaced slots till are shown instead of the cylindrical openings llt, while the core L shown in Figures 27 and 28 in general resembles the core H of Figures 21 and 22, differing therefrom in the use of the circumferentially spaced slots 5i instead of the holes 13.

Instead of utilizing the outside stop 32 for the contact arm, an inside stop may be provided as shown in Figures 310 and 31 where a lug or boss 45 is molded integrally with the base on the bottom surface of the recess 25 to cooperate with a stop arm i6 secured on the disc it at the inner end of the cylindrical block it. The stop arm it is shown as a right angular piece of metal which may be welded at the proper location on the disc it -to stop the movement of the Contact arm at the desired point; although obviously the stop arm might be adjustably mounted on the disc i6 in any suitable way.

In this forni of the invention, instead of the concavo-convex spring 22 of Figure 3, a helical compression spring @il is shown.

From the fore-going, it will be evident that the invention provides a rheostat of which the base and core can be rapidly, simply and neatly assembled and wherein the bond between the core and the base shall be of great mechanical strength. In this connection, it might be further pointed out that the post 2 serves as a re-v inforcement for the split ring core and the bonding material between the inner surface of the core and the outer surface of the post makes possible rapid conduction of heat away from the core. Also, the Ventilating passages in the core and the base or either one thereof provides for rapid and continuous cooling of the rheostat so that a rheostat of a given size will have a higher wattage rating than known rheostats of the same size without such ventilation. The outside' stop. 32 provides a simple and positive abutment for the contact arm as indicated by broken lines in Figure 2. The construction permits easy and quick assembly of the stop and contact member or collector ring t; and the stop block acts as a shield to separate the collector ring terminal 3l from the winding terminals 5. While `the stop has been shown as secured to the base by a bolt, obviously a screw, rivet or eyelet may be utilized as a fastener or the block could be secured to the base by vitreous enamel.

The block as shown could be interchanged with other blocks so that the Itop of the block would be level with or below the brush track surface so as to permit a 360 rotation of the contact arm; and if desired other electrical devices such as a limit switch could be secured on the sector shaped projection 3 in place of the stop block 32.

While I have shown and described several now preferred embodiments of my invention, it should be understood that this is primarily for the purpose of illustrating the principles of the invention and that the details of construction of the rheostat may be widely modified and changed within the spirit and scope of the invention,

I claim:

l, The combination of a ceramic base having a central post and a flange projecting laterally therefrom, a ceramic core encircling said post and secured thereto by vitreous enamel and with one end abutting said flange, a resistance Winding on said core, and means for connecting said resistance Winding in an electric circuit, said ange having air circulating holes therethrough and said core having air circulating recesses communicating with said holes.

2. The combination of a dielectric base, a dielectric core having a resistance Winding thereon With a brush track surface, said core being secured on said base with said track surface exposed and said core also having recesses therein opening through the surface thereof beneath said winding, and means including a contact arm and a brush slidable over said track surface for connecting said winding in a circuit.

3. The combination of a base having a post and a sector-shaped lug projecting from the side thereof, a split ring core mounted on said base in encircling relation to said post with said sector-shaped lug disposed in the gap between the ends of said split ring core, a resistance winding on said core having a brush track surface, means for connecting said resistance winding in a circuit including a contact arm rotatable coaXia-lly with said track surface and having a brush engaging said track surface, and a stop for said contact arm including a block mounted on said lug to be abutted by said con tact arm at the limits of its rotation.

4. The combination of a base having a post and a sector-shaped lug projecting from the side thereof, a split ring core mounted on said base in encircling relation to said post with said sectonshaped lug disposed in the gap between the ends of said split ring core, a resistance winding on said core having a brush track surface, means for connecting said resistance winding in a. circuit including a contact arm rotatable coaxially with said track surface and having a brush engaging said track surface, an annular contact member on said post having a terminal lying on said lug and a second brush on said contact arm engaging said contact mem- 7 ber, a .block secured on ,said lug and clamping said terminal between said yblock and :said lug, and .also disposed to be abutted by and thereby to stop said contact arm at the limit of its rotation.

5. The combination of a ceramic split ring core having a resistance winding thereon, a ceramic base having a vfrusto-conical post and a ange projecting from said post, said post extending into said core in closely spaced relation to the inner :surface of the core throughout a major portion of the height of the core'and said flange abuttingone end ofthe core, and a vitreous enamel between the side walls of the post and the inner surface of said ring core and .bonding said post, enamel and core together to provide for rapid conduction of heat from said core to said post and for reenforcement of said 'core by said post, and means for connecting said resistance winding in a circuit including a movable vcontact arm engaging said winding at lthe other fend of said core, said flange of the .base having air circulating holes Vtherethrough and said core having air circulating recesses lcom-- municating with -said holes.

References vCited in the le of this patent UNITED STATES PATENTS Number Name Date 1,823,474 Schellenger Sept. 15, 1931 2,021,487 McDonell et al. Nov. 19, 1935 2,040,278 Siegel May 12, 1936 

